We present a comprehensive analysis of the whole sample of available XMM-Newton observations of High Mass X-ray Binaries ( HMXBs ) until August , 2013 , focusing on the FeK \alpha emission line .
This line is a key tool to better understand the physical properties of the material surrounding the X-ray source within a few stellar radii ( the circumstellar medium ) .
We have collected observations from 46 HMXBs , detecting FeK \alpha in 21 of them .
We have used the standard classification of HMXBs to divide the sample in different groups .
We find that : ( 1 ) different classes of HMXBs display different qualitative behaviour in the FeK \alpha spectral region .
This is specially visible in SGXBs ( showing ubiquitous Fe fluorescence but not recombination Fe lines ) , and \gamma Cass analogs ( showing both fluorescent and recombination Fe lines ) .
( 2 ) FeK \alpha is centred at a mean value of 6.42 keV .
Considering the instrumental and fits uncertainties , this value is compatible with ionization states lower than Fe xviii .
( 3 ) The flux of the continuum is well correlated with the flux of the line , as expected .
Eclipse observations show that the Fe fluorescence emission comes from an extended region surrounding the X-ray source .
( 4 ) We observe an inverse correlation between the X-ray luminosity and the equivalent width of FeK \alpha ( EW ) .
This phenomenon is known as X-rays Baldwin effect .
( 5 ) FeK \alpha is narrow ( \sigma _ { line } < 0.15 keV ) , reflecting that the reprocessing material does not move at high speeds .
We attempt to explain the broadness of the line in terms of three possible broadening phenomena : line blending , Compton scattering and Doppler shifts ( with velocities of the reprocessing material V \sim 1000 km/s ) .
( 6 ) The equivalent hydrogen column ( N _ { H } ) directly correlates with the EW of FeK \alpha , displaying clear similarities to numerical simulations .
It highlights the strong link between the absorbing and the fluorescent matter .
( 7 ) The observed N _ { H } in Supergiant X-ray Binaries ( SGXBs ) is in general higher than in Supergiant Fast X-ray Transients ( SFXTs ) .
We suggest two possible explanations : different orbital configurations , or a different interaction compact object - wind .
( 8 ) Finally , we analysed in more detail the sources IGR J16320-4751 and 4U 1700-37 , covering several orbital phases .
The observed variation of N _ { H } between phases is compatible with the absorption produced by the wind of their optical companions .
The obtained results clearly point to a very important contribution of the donor ’ s wind in the FeK \alpha emission and the absorption when the donor is a supergiant massive star .